Create Drum Map Function

This feature generally works for me. I use both Groove Agent and EZ Drummer, and if I want to create a drum map, I can. But sometimes when click on NO DRUM MAP, the create drum map in the menu is faded. If I click on it nothing happens. There are options to choose from, including the GM map and other other drum kits I have tried or used, but today, for example, the one I was using was not one of these.
What should I do, or not do?

This feature needs to be supported by the Instrument. Unfortunately EZ Drummer doesn’t (yet), but you can load some Drum Maps for EZ Drummer from here:
http://www.toontrack.com/forum/studio-corner-1/where-can-i-download-the-cubase-drum-maps/page-2/

Or make your own like shown here:
https://youtu.be/rVLmi51HXuY

How did I miss that? I read your answer and thought, nah, it’s worked for some EZ kits, but no, I just missed the pattern.
Thanks I’ll work with the links.